Crown ethers polymers

The facile way by which zeolitic frameworks can be formed is further confirmed by their production imder acid and nonaqueous conditions, from the gas phase, and with organic additives as diverse as simple alcohols and amines, polymers, crown ethers, and dye molecules. 

Interfacial transfer reactions promoted by polymer crown ethers and cryptands proceed according to the same mechanism as for respective soluble catalysts. The reactions occur in the organic shell surrounded by the complexed ligand. Anions are exchanged on the surface of the water-organic solvent interface, whereby the exchange... 

Chiral stationary phases that are currently available can be classified into those containing cavities (cellulose derivatives, cyclodextrins, synthetic polymers, crown ethers, and chiral imprinted gels), affinity phases (bovine serum albumin, human serum albumin, a-glycoprotein, enzymes), multiple hydrogen-bond phases, Ti-donor and Ti-acceptor phases, and chiral ligand exchange phases. This classification scheme was used in a review that gave numerous pharmaceutical examples of separation by... 

A good deal of work has been done on polymeric crown ethers during the last decade. Hogen Esch and Smid have been major contributors from the point of view of cation binding properties, and Blasius and coworkers have been especially interested in the cation selectivity of such species. Montanari and coworkers have developed a number of polymer-anchored crowns for use as phase transfer catalysts. Manecke and Storck have recently published a review titled Polymeric Catalysts , which may be useful to the reader in gaining additional perspective. 

Most of the compounds in this class have been prepared from preexisting crown ether units. By far, the most common approach is to use a benzo-substituted crown and an electrophilic condensation polymerization. A patent issued to Takekoshi, Scotia and Webb (General Electric) in 1974 which covered the formation of glyoxal and chloral type copolymers with dibenzo-18-crown-6. The latter were prepared by stirring the crown with an equivalent of chloral in chloroform solution. Boron trifluoride was catalyst in this reaction. The polymer which resulted was obtained in about 95% yield. The reaction is illustrated in Eq. (6.22). 

It was noted early by Smid and his coworkers that open-chained polyethylene glycol type compounds bind alkali metals much as the crowns do, but with considerably lower binding constants. This suggested that such materials could be substituted for crown ethers in phase transfer catalytic reactions where a larger amount of the more economical material could effect the transformation just as effectively as more expensive cyclic ethers. Knbchel and coworkers demonstrated the application of open-chained crown ether equivalents in 1975 . Recently, a number of applications have been published in which simple polyethylene glycols are substituted for crowns . These include nucleophilic substitution reactions, as well as solubilization of arenediazonium cations . Glymes have also been bound into polymer backbones for use as catalysts " " . 

Cyclic low molecular weight compounds. Chiral separations using chiral crown ethers immobilized on silica or porous polymer resins were first reported in the... 

Lewis et al. [52,53] have also determined labile chlorines in PVC by a crown ether catalyzed acetoxylation of PVC and the thermal degradation characteristics of the modified polymer. The values were comparable with those obtained by the phenolysis method. 

It may not be appropriate to compare the thermal stability characteristics of VC/VAc copolymer to that of a VC homopolymer (PVC). The copolymerization would involve different kinetics and mechanism as compared to homopolymerization resulting structurally in quite different polymers. Hence, copolymerization of VC with VAc cannot be regarded as a substitution of chlorines in PVC by acetate groups. To eliminate the possibility of these differences Naqvi [45] substituted chlorines in PVC by acetate groups, using crown ethers (18-crown-6) to solubilize potassium acetate in organic solvents, and studied the thermal stability of the modified PVC. Following is the mechanism of the substitution reaction ... 

Fig. 6. Proton-driven transport of alkali metal ions through a membrane formed from 12-crown-4 polymer (43 n = 1) (crown ether content of about 30%). M+], and (M+fc refer to metal ion concentrations at time - i and 0, respectively. (Cited from Ref.471)...

There have been a number of different synthetic approaches to substituted PTV derivatives proposed in the last decade. Almost all focus on the aromatic ring as the site for substitution. Some effort has been made to apply the traditional base-catalyzed dehydrohalogenation route to PTV and its substituted analogs. The methodology, however, is not as successful for PTV as it is for PPV and its derivatives because of the great tendency for the poly(u-chloro thiophene) precursor spontaneously to eliminate at room temperature. Swager and co-workers attempted this route to synthesize a PTV derivative substituted with a crown ether with potential applications as a sensory material (Scheme 1-26) [123]. The synthesis employs a Fager condensation [124] in its initial step to yield diol 78. Treatment with a ditosylate yields a crown ether-functionalized thiophene diester 79. This may be elaborated to dichloride 81, but pure material could not be isolated and the dichloride monomer had to be polymerized in situ. The polymer isolated... 

Polymer supported xanthene derivatives have been used in the solid phase synthesis of 1-aminophosphinic acids, RCH(NH2)PH(0)0H, <%TL1647> and of C-terminal peptide amides <96JOC6326>. Xanthene units also feature in crown ethers <96JCS(P2)2091>, calixarenes <96JOC5670> and in a flexible template for a P-sheet nucleator <96JOC7408>. 

Polyphosphazenes bearing crown ethers (12-crown-4,15-crown-5 and 18-crown-6) as single or as mixed substituents with trifluoroethoxy or methoxy-ethoxyethoxy groups were synthesized by Cowie [601,602] and Allcock [484] and their conductivity studied because it was shown that the incorporation of crown ether molecules into a polymer electrolyte could increase their ionic conductivity. In these macromolecules, the crown ether units were linked to the backbone through oxymethylene spacer groups. 

Mathias, L. J. Carraher, C. E., Eds. Crown Ethers and Phase Transfer Catalysis in Polymer Science Plenum Press, New York,... 

Crown ethers are cyclic polymers of ethylene glycol such as 18-crown-6 ... 

Gibson et al. [109] and Sjen et al. [110] reported pseudo-polyrotaxanes and polyrotaxanes consisting of crown ethers with various polymers. The resulting polyrotaxanes were nonstoichiometric. Their properties - including solubility and glass transition temperatures - were different from those of the starting polymers. 

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